1. Field of the Invention
This invention is of application in the metal elimination that contaminates soils and aquatic zones.
2. State of the Art
At present, the state of the art provides alternative ways of solving the problem. The most habitual are also the costliest and they base on, fundamentally chemical and physical methods, as they are: the committal of the contaminated soils with inert materials, the cleanliness “in situ” with the machines and chemical suitable material, the storage as poisonous residues in the places regulated for it (with correspondent license), etc.
In the United States there have been carried out experiences of recovery of the contaminated soils, using natural plants, of the type of the corn, tomato, sunflower, Brassica juncea, etc., and trees principally willow and black poplar. Most of these pioneering experiences has been realized by the American army moved by the desire to recover soils been contaminated with the metallic garbage that provoke the bullets that are in use in the tests of shot. These metals contain fundamentally lead.
Also another type of experiences have been performed in New Jersey. It was carried out a selection of cultures of Brassica juncea (Brassica juncea (L) Czem) with aptitude to accumulate the elected metals; it was used enmendants of the soil or chelants substances. Later they allowed them to glow, and to be harvest, and the contain in metals have been analyzed. In these two cases, the used techniques have been fundamentally: treatment of contaminated soils, and regeneration by metal accumulation in the cultivated plants. The “U.S. Environmental Protection Agency”, also acquaintance as EPA, has been the pioneering institution in the study of these processes of phytoremediation. Together with the company “Phytotech” was the manager of realizing the mentioned process of recovery of the contaminated soils in New Jersey. In the experiments in which the objective has been the recovering of munition, as the one mentioned above, it has participated actively the engineers' body of the American army (Army Corps of Engineers). The company Phytotech is one of pioneers in the whole world. In Spain there exist references of ELECNOR, which it applies technologies of bioremediation patented by the North American company ECS.
Some examples of vegetable used material:                hybrid trees of black poplar have been in use for extracting nickel, cadmium and zinc of contaminated soils (University of Georgia, USA, “Savannah River Ecology Laboratory”).        In the department of energy of Ashtabula, Ohio, plants of sunflower have been in use for remediation of soils and waters contaminated by uranium.        
Some examples of important patents are the following ones:                U.S. Patent. Phytorecovery of metals using seedlings. U.S. Pat. No. 911,655, Aug. 15, 1997, Phytotech, Inc. (Monmouth Junction, N.J.).        U.S. Patent. Method of using pelargonium sp. as hyperaccumulators for remediating contaminated soil. U.S. Pat. No. 185,797, Nov. 4, 1998, University of Guelph (Guelph, Calif.).        U.S. Patent. Methods for removing pollutants from contaminated soil materials with a fern plant. U.S. Pat. No. 546,941, Apr. 11, 2000, University of Florida (Gainesville, Fla.). The invention describes the use of a variety that is less extensive geographically that N glauca. It is a question of a fern that basically accumulates enormous quantities of arsenic. Methods are described to carry out the decontamination using one or different varieties of ferns. The use of this type of plants has fundamentally the disadvantage of which there is located in very humid habitats which limits his use. Besides the need to receive very much water contribution can have negative effects for the soil where they grow since, on having contributed big quantities of water, this one can displease the metals at deeper levels or spread them.        
Since it parts with the information contributed in the exposed patents, the work it has centred on processes of bioremediation, especially using hyperaccumulators (those plants that possess an extraordinary capacity of absorption of metals, and of accumulation in his biomass).
The phytoremediation consists basically of the use of plants or of vegetable material, to decontaminate soils with high concentrations of harmful elements. Recently a review has been realized, about the topic, by two Spanish investigators, in the publication: “Phytoextraction: to cost-effective plant-based technology for the removal of metals from the environment”. Carlos Garbisu, Itziar Alkorta. Bioresource Technology 77 (2001) 229-236. Where the state of the investigation is described in phytoremediation, topcoat being based on the concrete aspect of the phytoextraction.
One key article (review), for the importance of the works realized by the authors are the followings:    Chaney, R. L., Malik, M., Li, Y. M., Brown, S. L., Brewer, E. P., Angle, J. S., Baker, A. J. M., 1997. Phytoremediation of soil metals. Current Opin. Biotechnol. 8, 279-284.    Salt, D. E., Smith, R. D., Raskin, I., 1997. Phytoremediation of soil metals. Current Opin. Biotechnol. 8, 279-284. This is an article of reference for the punctual contribution andCorn and buckthorn are two species that accumulate lead. (Huang, J. W., Cunningham, S. D., 1996. Lead phytoextraction: species variation in lead uptake). As for the cadmium, Salix viminalis, Thlaspi caerulescens and Alyssum murale seem to be the best species (SALIX EXPERT PHYTOEXTRACTOR, Maria Greger, Dept of Botany, Stockholm University, S-106 91 Stockholm, Sweden).
Concerning to the molecular biology of metal absorption, fundamentally researchers have worked with plants of the genre of Brassica, and among them especially Brassica juncea. In these type of plants genetic transformations have been realized by means of skills of biotechnology. Also they have been carried out in another type of vegetable varieties as black poplar and certainly Arabidopsis. Regarding the genes that have been in use for decontaminating heavy metals, it is necessary to distinguish basically three families: metallothioneins, phytochelatins, and genes that regulate the processes of oxidation-reduction. It is necessary to emphasize the pioneering work realized with bacterial genes that are specialized in the absorption of mercury, which marked a milestone in this field: Rugh, C. L., Wilde, H. D., Stack N. M., Thompson, D. M., Summers, A. O., Meagher, R. B., 1996. “Mercuric ion reduction in transgenic Arabidopsis thaliana plants expressing to modified bacterial mere gene”. Proc. Natl. Acad. Sci. USA 93, 3182-3187.
The most important works in this field, apart the mentioned one, have been carried out by Schroeder, Rea, and Therry. During the same year, Schroeder studied for the first time the enzyme produced by the gene TaPCS1, which is a phytochelatin of wheat. (The EMBO Journal Vol. 18 Not 12 pp. 3325-3333, 1999. “Tolerance to toxic metals by to gene family of phytochelatin synthases from plants and yeast”. Stephan Clemens, Eugene J. Kim, Dieter Neumann and Julian I. Schroeder). The second one cloned, the homolog phytochelatin of Arabidopsis (Proc. Natl. Acad. Sci. USA, Vol. 96, pp. 7110-7115, June 1999). “AtPCS1, to phytochelatin synthase from Arabidopsis: Isolation and in vitro reconstitution”. Olena K. Vatamaniuk, Stéphane Mari, Yu-Ping Lu, and Philip A. Rea). And the third one transformed in several occasions, Brassica juncea with genes that increase the metal absorption (“Cadmium Tolerance and Accumulation in Indian Mustard Is Enhanced by Overexpressing γ-Glutamylcysteine Synthetase”. Yong Liang Zhu, Elizabeth A. H. Pilon-Smits, Alice S. Tarun, Stefan U. Weber, Lise Jouanin, and Norman Terry. Plant Physiology, December 1999, Vol. 121, pp. 1169-1177).